1. Field
The present invention relates generally to the operation of wireless communication devices, and more particularly, to methods and apparatus for generating, maintaining, and searching a list of pilot signals in a wireless communication network.
2. Background
In modern wireless communication devices, such as cellular telephones, there is sometimes a need to determine the energy levels of pilot signals that are received by the wireless communication device. The wireless communication device can then determine which base station to communicate with based on at least the energy levels of the received pilot signals. In some such wireless communication devices, a list of pilot signals and associated energy levels is maintained and continually updated to ensure that the wireless communication device can make the best decision as to which base station through which to communicate. This list is sometimes referred to as a neighbor list.
Generally, many neighbors can be stored in the memory of a wireless communication device. For example, in one case, up to 40 neighbors can be stored. Typically, not all of the neighbors can be searched at one time due to the deleterious effect on the device's battery life. For example, in a device that stores 40 neighbors, a search queue is used to store, for example, up to 16 neighbors (i.e., 16 searches). In this example then, searching the 40 neighbors would be performed using three arbitrary search queues or lists. If there is still time left when all three queues are finished, processing reverts back to the first queue and the process is repeated. Otherwise, if there is not enough time to finish all the queues, the current search queue (whichever queue that may be) is aborted and processing terminates.
In some cases, partial searching is not available, meaning that results are generated for all neighbors in the queue, or no data is generated. This can happen if the window sizes for the neighbors are big while the device is operating in a quick-paging mode, sometimes referred to as QPCH mode. In some systems, there is a very small amount of time on the order of milliseconds for searching in the QPCH mode. If 16 pilots each with a large search window (worst case) are placed in the search list, the search will take too long to complete. Since this search will not be completed in the available time, the search will be aborted and no search data will be obtained.
Since it may seem that using large window sizes causes the search problem described above, the solution appears to be to search using a smaller window. However, using smaller window sizes may also risk missing good pilot signals that are outside of the smaller window range, due to differential propagation delays in large cell radius situations. Thus, serious problems may occur when base stations are spread out over large geographic areas where large windows are really needed to receive the far multipaths.
Therefore, what is needed is a system that operates to search for pilot signals in a wireless network where the quantity of searching is adjusted to fit within the available search time, with the attempt to minimize device ‘awake’ time. The system should also operate to reduce the window size necessary for searching selected pilot signals allowing either more pilots to be searched within a given time interval, without missing good pilot signals that are outside of the smaller window range, or allowing the device to remain awake for a shorter period of time, reducing battery consumption.